If you didn't make anyone else have the power to do that then you would be safe.  Never give anyone you don't know personally power over your forum.  And then think twice about them.

SMF For Free has actually tried this before. It turned out to be more work than it was worth.

The only way to make it safe was to have it so that people could enter their forum, username and password. Problem is creating something that can check the password and username outside of the SMF For Free software without security risks.

SMF For Free is recently finding trouble reinstating power to forums. Too many requests, too many problems and too many risks with the size of this service.

It's always a risk, which is why you should always be sure. If you aren't sure, don't give them the full power. You don't have to anyways.

There is just no need at all for a small forum to have 4 Admins, 6 Moderators, 3 Global Moderators.     I am the only Admin on my own forum.   If my forum were to get a lot busier then it currently is I would decide upon having moderators to help out with the posts, threads, things like that.    You make someone Administrator -  you give them complete control of your forum.   We can not always guarantee that should you lose that control that it can be returned to you.